1. Field of the Invention
The present invention relates to a method of and apparatus for reducing the amount of smoke emitted from a diesel engine.
2. Description of the Related Art
Diesel-engined construction machines designed to operate in enclosed spaces such as tunnels have heretofore been equipped with a so-called catalytic muffler for oxidatively removing such harmful components as HC and CO that are contained in the exhaust gas emitted therefrom. The conventional catalytic muffler i s, however, incapable of removing black smoke particles from exhaust gas, and the fact is that black smoke particles are released into the atmosphere.
To solve this problem, a method has been proposed wherein black smoke particles are trapped by means of a honeycomb type -- ceramic filter and the particles trapped in the ceramic filter are burned for regeneration by means of the heat of the exhaust gas. Such a method is, for example, disclosed in "Diesel Particulate Control" in Automotive Engineering, November 1984, page 63 - 70, published by the Society of Automotive Engineers Inc. in 1984, and "Diesel Motorcar Exhaust Gas and Countermeasures therefore" in Machine Research, Vol.39 No.10, page 1103 - 1104, published by the Japan Machinery Institute in 1987. The method disclosed in these prior art publications suggests the use of a catalyst on the walls of gas -- flow passages of the ceramic filter in order to lower the combustion temperature of black smoke and throttling of a butterfly valve in order to raise the temperature of the exhaust gas, since the temperature of the exhaust gas is not always sufficient to burn the trapped particles.
These prior arts, however, only teach trapping and burning of the black smoke particles in a conceptional manner and do not teach how an actual system capable of carrying out the method should be realized in an actual vehicle. In an actual vehicle, e.g., a construction machine, if the butterfly valve is throttled too much, the machine would readily stop and operations would have to be discontinued. There has, therefore, been a strong demand for an improved method and apparatus wherein trapping and burning of black smoke particles is automatically controlled without causing any engine trouble so that it will be possible to realize practical system for actual working machines and vehicles which does not disturb the operation thereof.